The tetra- and mono-thionated cyclic octadepsipeptides represent novel cyclic octadepsipeptide derivatives with broad-spectrum activity against parasitic nematodes in mice and sheep. Some of these show better activity than the potent natural anthelmintic cyclic octadepsipeptide PF1022A against Hymenolepis nana, Heterakis spumosa and Trichinella spiralis larvae in mice. In particular, they show improved efficacy against Haemonchus contortus and Trichostrongylus colubriformis in sheep compared with PF1022A. Here we report on two different and simple synthetic pathways for this new class of thionated cyclic octadepsipeptides.

The proton affinities ( P A ) of all isomeric dimethylacetophenones were determined using the 'kinetic method' with a tandem mass spectrometer and by measurements of the proton transfer equilibrium in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. For both methods acetophenone and p-methylacetophenone, with well known PA values, were used as reference bases. Both methods yielded identical PA values for all dimethylacetophenones. The PA of the dimethylacetophenones were in a narrow range between 872 and 880 kJ mol-' except for 2,6-dimethylacetophenone, for which a PA of 856 kJ mol-' was found. The results are discussed in terms of possible mesomeric structures stabilizing the positive charge with regard to the substitution pattern in the phenyl ring. Obviously, the significant smaller PA of 2,&dimethylacetophenone compared with the other isomers is due to the distortion of the conjugation of the C-0 double bond with the aromatic n system.

Protonated aromatic aldehydes and methyl ketones la-lOa, carrying initially the proton at the carbonyl group, are prepared by electron impact-induced loss of a methyl radical from 1-arylethanols and 2-aryl-Bpropanols, respectively. The aryl moiety of the ions corresponds to a benzene group, a naphthalene group, a phenanthrene group, a biphenyl group, and a terphenyl group, respectively, each substituted by a CH30CH2 side-chain as remote from the acyl substituent as possible. The characteristic reactions of the metastable ions, studied by mass-analyzed ion kinetic energy spectrometry, are the elimination of methanol, the formation of CH,OCH$ ions, and the elimination of an ester RCOOCH, (R = H and CH,). The mechanisms of these fragmentations were studied by using D-labeled derivatives. Confrrming earlier results, it is shown that the ester elimination, at least from the protonated aryl methyl ketones, has to proceed by an intermediate [acyl cation/arylmethyl methyl etherl-complex. The relative abundances of the elimination of methanol and of the ester decrease and increase, respectively, with the size of the aromatic system. Clearly, the fragmentation via intermediate ion-neutral complexes is favored for the larger ions. Furthermore, the acyl cation of these complexes can move unrestricted over quite large molecular distances to react with the remote CH30CH,-side-chain, contrasting the restricted migration of a proton by 1,2-shifts ("ring walk") in these systems. (J Am Sot Mass Spectrom 1992, 3,[417][418][419][420][421][422][423][424][425][426]

Field experiments employing yellow water-traps with vials releasing methyl salicylate, butyl isothiocyanate, 4-pentenyl isothiocyanate and diethyltoluamide were conducted during the spring migration of Phorodon humuli (Schrank), with the aim of identifying substances which might be used in the field to deter landing on hop plants. Methyl salicylate and the two isothiocyanates reduced trap catches of P. humuli. During the spring of 1994 a slowrelease formulation of methyl salicylate and a /?-acid-rich hop resin sprayed on to hop plants did not reduce aphid infestations significantly. In autumn cis,cis-nepetalactol, the main component of P. humuli's sex pheromone, prepared by various synthetic routes, increased trap catches of males and gynoparae equally. Catches of males in pheromone traps situated in a hop garden decreased with increasing trap height. Catches of males in traps charged with increasing doses of the cis,cisnepetalactol peaked at 1 mg and then plateaued, whereas catches of gynoparae peaked similarly at 1 mg and then decreased. The effects of kairomones from an extract of the primary host, sex pheromone and a visual cue from yellow compared with clear water-traps were additive. The prospects for developing a semiochemicals-based control strategy against P. hurnuli, using some or all of the above elements, are discussed.

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